Notorious software bug was killing people 40 years ago — at least three people died after radiation doses that were 100x too strong from the buggy Therac-25 radiation therapy machine

The Therac-25 radiation therapy machine, plagued by a software bug in 1985, delivered fatal radiation doses to at least three patients due to a race condition issue. The bug allowed operators to mistakenly choose the wrong treatment mode, resulting in overdoses. The machine's software-only controls lacked hardware interlocks found in earlier models, contributing to the accidents. The incidents led to calls for improved testing and documentation in medical software development, making Therac-25 a cautionary tale in computer science education.